1. Field of the Invention
This invention relates to wafer planarization technology for planarizing the thickness distribution of a semiconductor wafer by local dry etching of a relatively thick portion of the semiconductor wafer with activated species gas.
2. Description of Related Art
FIG. 1 is an explanatory diagram for explaining a wafer planarization method and apparatus by means of local dry etching method with plasma. In FIG. 1, reference numeral 100 denotes a plasma generator, and activated species gas G in plasma generated in the plasma generator 100 is injected on the surface of a semiconductor wafer W from a nozzle 101. The semiconductor wafer W is placed and fixed on a stage 120, and the stage 120 is moved (scanned) horizontally at a controlled speed with respect to the nozzle 101.
The thickness of the semiconductor wafer W is different locally. Prior to local dry etching process, the thickness of divided local areas of the semiconductor wafer W is measured to obtain position data of individual areas and thickness data of the positions (position-thickness data).
The amount of removed material of respective local areas removed by local dry etching depends on the exposing time period to activated species gas G and etching profile (removing speed distribution) of a local area. Based on the above, the relative speed (nozzle-wafer relative speed) to be applied when the nozzle passes over the respective local areas is calculated so that the wafer surface is planarized throughout, and the respective local areas are scanned at the calculated speed and pitch to planarize the entire surface of the wafer. At this occasion, the nozzle moves slow on the relatively thick portion and convex portion (relatively thick portion) Wa, and moves fast relatively on the relatively thin portion.
The surface of a semiconductor wafer is uneven with various levels as shown in FIG. 2, and the unevenness causes a low yield in semiconductor device production. Among these unevennesses, an unevenness called as flatness has the spatial wavelength of about λ=10−2 m or larger level and wave height of h=10−7 to 10−5 m level. This unevenness is a target to be processed by a local dry etching apparatus. An unevenness called as nanotopography has the distribution center at the spatial wavelength of about λ=10−3 m level and wave height of about h=10−8 m level. Further, an unevenness called as micro-roughness has the distribution center at about λ=10−6 m level and wavelength of about h=10−9 m level.
A flatness measurement apparatus not only measures the above-mentioned flatness level but also detects smaller unevenness for the wavelength and wave height generally. The measurement result obtained from a flatness measurement apparatus has been used as it is as the basic data for calculating the nozzle-wafer relative speed formerly, and the measured nozzle-wafer relative speed value includes excessive acceleration and deceleration. Such nozzle-wafer relative speed that is input to a dry etching apparatus as the command value results in frequent acceleration and deceleration of a drive motor.
FIG. 3 is a graph obtained by plotting a command value (input speed) of the nozzle-wafer relative speed and the measured stage moving speed when a nozzle moves from one end to the other end of a diameter of a wafer having a diameter of 200 mm. FIG. 3 shows that there is large speed difference d between the measured value and command value and the nozzle-wafer relative speed cannot follow the command value exactly. The speed difference is absorbed in the form of instantaneous overload or out-of-step of a drive motor in a dry etching apparatus or deformation of some members of the dry etching apparatus. Such frequent acceleration and deceleration results in severe load on the drive motor and movable parts, and causes poor process precision and short machine life while the machine is used for a long time.